Aeration apparatuses are used in applications for, for example, preventing the unintended decomposition of liquids by increasing the dissolved oxygen content in wastewater from sewage treatment plants, wastewater treatment plants in food factories and livestock farms, and wastewater treatment facilities in other types of factories, as well as by increasing the dissolved oxygen content in liquids found in ponds, rivers, culture ponds, and the like. The gas-liquid mixing apparatus disclosed in Patent Literature 1, which was filed by the inventors of the present invention, is known as a conventional aeration apparatus. This apparatus includes a pentagonal gas-liquid mixing cylinder whose top and bottom are open, collision blades disposed in multiple stages within the gas-liquid mixing cylinder, and a gas ejection nozzle disposed at a bottom area of the gas-liquid mixing cylinder, and is configured such that gas ejected from the gas ejection nozzle swirls upward through the gas-liquid mixing cylinder while colliding with the collision blades, so the gas is broken into fine bubbles and dissolves into the liquid.